Don't think Sandro has been given enough of a chance in a side that's performing. No need to sell yet.
Niasse and Mirallas are the only ones I want sold, though there are plenty that I'd listen to offers for.
Edit: Oh, and Klassen. I realise it goes against my point about Sandro, but get rid. Expensive mistake that is far too lightweight for the English game. Guy's like a wet flannel.